This proposal is aimed in part at utilizing the diversity of ultrastructural features of bacterial cells to assist in their identification and taxonomic classification. This will be accomplished by comparing ultrastructural data with serological relatedness and biochemical characteristics for certain bacteria isolated from human mouths with and without periodontal lesions. Specific antibodies will be produced in rabbits against a selection of microorganisms which appear to predominate in periodontal lesions. These antibodies will be used to test the feasibility of localizing these bacteria in microbial smears obtained from the gingival sulcus or pocket area of human subjects or in pure cultures of bacterial isolates. The presence of circulating antibodies in the serum of human volunteers to the same selection of microorganisms will be tested by the indirect F.A. technique. Evidence will be sought for trends in labeling patterns which may be of value in the diagnosis and monitoring of clinical problems. The long term objective is to gain a better understanding of the microbial flora associated with periodontal disease, to learn how the flora and the periodontal lesion may vary in terms of the immune response of the host, and to develop practical means of identifying specific microbial components of the periodontal flora and circulating antibodies to these bacteria which may be of value for monitoring the severity and course of periodontal disease.